For some time, solid-plate electric surface heating elements have been in wide usage in Europe and, more recently, they have gained some consumer acceptance in the United States. These elements have been referred to by a variety of names such as, for example, solid-surface electric heating elements, sealed electric heating elements, and Euro-style or European range top elements. One advantage of these elements is that they are sealed to the cooktop and have a solid surface so that spill-overs don't run underneath the cook top. Also, some like the appearance of the solid plate elements.
Generally, a solid plate element has a substantially flat cast iron top disk or plate with a trim ring for supporting the element from the cook top or main top onto which it is sealed. Extending downwardly from the underside of the top disk is a cylindrical casing which encloses a ceramic layer in which resistive electric heating coils are embedded. Encasing the lower end of the cylindrical casing is a bottom metal jacket or cover. Extending axially downwardly from the underside of the top disk is a grounding bolt which inserts through an aperture in the bottom jacket. A nut is tightened down on the bolt to hold the jacket in place.
In the prior art, a bracket is attached to the underside of the jacket and extends radially. A ceramic insulator terminal is then mounted on the outward end of the bracket. Uninsulated wire leads which are connected to one or more of the embedded resistive electric heating coils are fed through the bottom jacket via a ceramic block insulator and are run out to the ceramic insulator terminal. The first step for installing the solid plate elements in a range top has been to connect the power lines from the control unit to the ceramic insulator terminal and tightening down connecting screws to securely couple them to the respective wire leads. The solid-plate elements are then mounted within a cook top box by inserting them through respective apertures in the top platform where they are supported by the trim rings. The grounding bolts and locating posts extend through respective apertures in the floor of the cook top box or compartment and nuts are tightened down to securely fix them in place. Solid plate surface heating elements have also been mounted in plug-in cartridges that encase at least two elements.
The above-described range configuration and fabrication method have significant drawbacks for range manufacturers. First, if the range manufacturer is also in the business of manufacturing electric ranges with the much more common open coil surface heating elements that have a shielded spiral wire, the cook tops or main tops are generally not interchangeable parts. More specifically, with a range having shielded spiral wire or open coil surface elements, it is desirable to have a hinged lift-up cook top to permit fast and easy clean up of spill-overs. However, with the solid-plate elements, the cook top must be a box-type structure because the unshielded wires must be securely encased and the elements must be bolted in place and grounded.
Another drawback is that the initial fabrication and later maintenance for a solid plate element are much more complicated than for an open coil heating element. For example, rather than the consumer being able to merely lift a failed element out from the top and replace it as is done with an open coil or shielded spiral wire surface element, a service call is generally required with a solid plate element because it must be unbolted from the bottom and rewired. It is also a drawback that the open coil and solid plate surface elements are not interchangeable; some consumers who already own a range with one type of surface heating element may wish to switch to the other type.
Solid plate heating elements have also exhibited other disadvantages in the above-described prior art configuration. First, because the solid plate heating elements have been securely attached to the cook top or main top on which they are supported, the thermal conductivity from the solid plate heating element to the adjacent cook top has been relatively high and, as a result, cook tops have gotten very hot such as, for example, 270.degree. F. Another disadvantage is that solid plate heating elements generally have more mass than open coil heating elements, and therefore they are slower to heat up. For example, a solid plate heating element may take 30% longer to heat up than an equivalent open coil heating element. In fact, one important reason for originally using the open coil element was that it had relatively low mass and therefore heated up quickly. Thus, they were called high speed elements.